With respect to an EDFA (Erbium-Doped Fiber Amplifier) or the like which is used for, for example, a relay point in a main-line transmission path, and amplifies a signal, an optical module having a semiconductor laser and an optical fiber assembled therein is used as an exciting light source. The optical module of this type has a structure shown in FIG. 11A. In other words, a substrate 1 is placed on a Peltier element 12 in a box member 11, and a semiconductor laser chip 21 is fixedly secured to the substrate 1 through a sub-mount 7, an optical fiber 31 is fixedly secured thereto through an optical transmission member securing base 3a, a light receiving element 6 is fixedly secured to the substrate 1 through a light receiving element securing base 6a. Here, the optical transmission member securing base 3a and the optical fiber 31 are secured to each other by using a soldering material 5 or through a YAG welding process or the like (for example, see JP-A No. 7-333472).
In the optical module of this type, there have been demands for increasing the coupling efficiency between the semiconductor laser chip 21 and the optical fiber 31 to not less than 80% in order to reduce the load imposed on the semiconductor laser chip 21. In an attempt to achieve this value, the positional precision of the optical fiber 31 with respect to the semiconductor laser chip 21 needs to be set to approximately not more than ±0.2 μm. In the assembling process between these semiconductor laser chip and optical fiber, for example, as shown in FIG. 11B, the positioning between these members is carried out while detecting the output of the optical fiber 31 by a light output measuring device 41 so that these members are secured to each other through welding by a YAG laser or soldering.
Additionally, with respect to this positioning process, another method has been proposed in which image-pickup cameras are used for observing the positional relationship between the semiconductor laser chip 21 and the optical fiber 31 by picking up images in two directions from the upper face side and the side face side that is orthogonal to this side of the semiconductor laser chip 21 so that the positioning process is carried out by using photographic images (for example, see JP-A No. 6-281846 (FIG. 1)).
However, in the case when, after the positioning process using these methods, an optical transmission member such as an optical fiber is secured, a positional deviation actually occurs during the securing process. For this reason, it is necessary to correct the positional deviation during the securing process. However, for example, in the case of the securing process through welding by a YAG laser, there occurs a great positional deviation during the securing process, and little correction is made. Additionally, since the correction of the amount of deviation cannot be carried out quantitatively, the amount of deviation after the securing process reaches approximately 0.7 μm in average, as shown in FIG. 11C, resulting in a serious reduction in the yield. Moreover, since the correction process is carried out by preparing an increased number of welding points and by pulling toward the points, the number of corrections is limited to several times.
In contrast, in the case when the securing process is carried out by using a soldering material or the like, although the corrections can be carried out a desired number of times, the deviation direction of the optical fiber and the absolute amount of deviation are not recognized, with the result that, in spite of a number of corrections with high costs, it is not possible to carry out a complete positioning process.
Moreover, in the case when the securing process of the optical fiber is carried out through soldering, although this method is advantageous in that upon occurrence of a positional deviation, the correction is easily carried out by again fusing the soldering material, the application of the soldering material causes the possibility that heat, generated upon fusing the soldering material at the time of securing the optical fiber, is transmitted to the semiconductor laser chip to cause degradation in the characteristics of the semiconductor laser chip.